Stereophony is a popular spatial audio reproduction format. Stereophonic signals can be produced by in-situ stereo microphone recordings or by mixing multiple monophonic signals as is typical in modern popular music. This type of material is usually intended to be reproduced with a matched loudspeaker pair in a symmetrical arrangement as suggested in ITU-R BS.1116[1997] and ITU-R BS.775-1 [1994].
If the above recommendations are met, the listener will perceive an auditory scene, described in Bregman [1994], comprising various virtual sources, phantom images, extending, at least, between the loudspeakers. If one or more of the ITU recommendations are not met, a consequence can be a degradation of the auditory scene, see for example Bech [1998].
It is very typical to listen to stereophonic material in a car. Most modern cars are delivered equipped with a factory-installed sound system consisting of a stereo sound source, such as a CD player, and 2 or more loudspeakers.
However, when comparing the automotive listening scenario with the ITU recommendations, the following deviations from ideal conditions will usually exist:    (i) The listening positions are wrong;    (ii) The loudspeaker positions are wrong;    (iii) There are large reflecting surfaces close to the loudspeakers.
At least for these reasons, the fidelity of the auditory scene is typically degraded in a car.
It is understood that although in this specification reference is repeatedly made to audio reproduction in cars, the use of the principles of the present invention and the specific embodiments of systems and methods of the invention described in the following are not limited to automotive audio reproduction, but could find application in numerous other listening situations as well.
It would be advantageous to have access to reproduction systems and methods that, despite the above mentioned deviations from ideal listening conditions, would be able to render audio reproduction of a high fidelity.
Auditory reproduction basically comprises two perceptual aspects: (i) the reproduction of the timbre of sound sources in a sound scenario, and (ii) the reproduction of the spatial attributes of the sound scenario, e.g. the ability to obtain a stable localisation of sound sources in the sound scenario and the ability to obtain a correct perception of the spatial extension or width of individual sound sources in the scenario. Both of these aspects and the specific perceptual attributes characterising these may suffer degradation by audio reproduction in a confined space, such as the cabin of a car.